With an areal light source, for instance a coiled filament and a smooth reflector surface, local brightness variations occur in the film window due to imaging of the filament. It has been proposed to roughen the reflector surface by knurling or facetting. A reflector having a surfce of numerous small reflective areas is described for instance in the U.S. Pat. Nos. 4,021,659 and 4,035,631. Other surface structures are described, among others, in German Disclosure Document Nos. DE-OS 21 48 478 and DE-OS 23 63 378 to which U.S. Pat. No. 3,758,770, Morasz and 3,825,742, Levin, correspond. The structures of the reflector surface described therein cause the beams to fan out or spread more than with a smooth reflector surface. Thus, the image of the filament structure in the film window is blurred, but a certain non-uniformity in the film window illumination remains nevertheless. As a result of the increased stray light, the utilized light flux falls. This has to be compensated by increasing the power input of the lamp; this, in turn, causes a higher temperature in the film window than with smooth reflector surfaces. The common feature of all these solutions is that the reflectors have one contour only.